1. Field of the Invention
The present invention relates to a method of and an apparatus for measuring the attitude angles of a tongue of a head suspension installed in a hard disk drive, the tongue of the head suspension supporting a read/write head to read and write data from and to a disk driven in the hard disk drive.
2. Description of Related Art
When reading and writing data from and to the disk with the head suspension, the hard disk drive rotates the disk at high speed so that a slider, which is an element of the head suspension to hold the read/write head, slightly flies from the surface of the disk,
To densely record data on the disk, the slider of the head suspension must realize a low fly height. For this, the slider must minimize variations in static attitude angles, i.e., pitch and roll angles. During the manufacturing of the head suspension, the pitch and roll angles of the slider are measured to see if they are within tolerances.
Measuring the pitch and roll angles of the slider is usually carried out by measuring, in a noncontact manner, the pitch and roll angles of the tongue of the head suspension to which the slider is attached. For example, Japanese Unexamined Patent Application Publication No. 2002-074630 uses a laser displacement gauge to emit laser beams to multiple spots on a flat metal surface of the tongue to which the slider is going to be attached, finds the heights of the spots according to reflected beams, and measures the pitch and roll angles of the tongue according to the heights. U.S. Pat. No. 6,747,267 uses an autocollimator to emit a laser beam to a single spot on the surface of the tongue, obtains the position of a reflected beam, and measures the pitch and roll angles of the tongue according to the position.
Each of these related arts employs reflected beams from the surface of the tongue, and therefore, requires the surface of the tongue to be exposed to laser beams, i.e., not to be covered with anything.
Recent hard disk drives are miniaturized and sophisticated and sliders used for them are provided with a variety of functions, e.g., a fly height control function with thermal expansion, a heat assist function against thermal fluctuation in magnetization, and a disk contact detection function using a sensor.
For these additional functions, the slider must have not only original read/write wiring but also additional function wiring, interleaved wiring, ground wiring, and the like. As a result, a tongue of a head suspension to which the high-function slider is attached must have an increased number of electrodes (pads) to connect the various kinds of wiring required for the slider. These electrodes are arranged on the surface of the tongue as explained in, for example, U.S. Pat. No. 6,985,332 and No. 7,929,248.
More precisely, the electrodes are arranged on an insulating layer formed on the surface of the tongue. Namely, the surface of the tongue is covered with the electrodes and insulating layer.
As a result, there is left little or no exposed space on the surface of the tongue to receive laser beams. This makes the measurement of pitch and roll angles according to the related arts unachievable.
The related art that measures the pitch and roll angles of a tongue with an autocollimator tries to minimize the diameter of a laser beam by choosing an aperture diameter and a laser frequency, This is to make the laser beam avoid patterns made by adhesives, wiring, and insulating layers on the tongue.
Even with such a laser beam of minimized diameter, it is hard to measure the pitch and roll angles of a tongue if the tongue has many electrodes used for a slider.